Clinicians and veterinarians often select antibiotic therapies for infections on the basis of laboratory test results. The laboratory tests, known as antimicrobial or antibiotic susceptibility tests, determine the inhibitory activity of antibiotics against the microorganisms that cause infections. If the antibiotic susceptibility test indicates that an antibiotic is sufficiently potent to treat an infection, the microorganism causing the infection is reported to be "susceptible" to the antibiotic. If the test indicates a lack of sufficient antimicrobial potency for successful therapy, the microorganism is reported as "resistant" to the antibiotic. In some tests other categories of susceptibility may also be reported, e.g. "moderate susceptibility" or intermediate susceptibility."
A problem with currently available antimicrobial susceptibility tests is their failure to reliably predict the outcome of therapy. Sometimes an antibiotic will fail to cure an infection even though the microorganism is susceptible to the antibiotic in the laboratory test. That is, the current routine laboratory tests can be misleading and give an over-optimistic impression of the therapeutic potential of antibiotics. These tests can therefore cause patients to be given ineffective treatments. In serious infections, this inadequacy of current laboratory tests can have fatal consequences.
There are many explanations for failures of antibiotic therapies that were initiated on the basis of antibiotic susceptibility tests. Some involve patient-related factors and are idiosyncratic for certain types of patients or infections. However one explanation is error arising from a deficiency in the antibiotic susceptibility test itself. The antibiotic susceptibility tests that are currently in routine use do not adequately detect the antibiotic-inactivating potential of some microorganisms. Some microorganisms produce enzymes that inactivate antibiotics. Such enzymes, which are not reliably detected in routine antibiotic susceptibility tests, may cause sufficient antibiotic inactivation at the infective site in a patient to cause a treatment failure. The currently used antibiotic susceptibility tests, which measure only the antimicrobial activity of antibiotics and not the ability of microorganisms to cause antibiotic inactivation, fail to take into account this very important determinant of the outcome of therapy. This deficiency in the tests places clinicians at a disadvantage in selecting the most appropriate antibiotic for their patients.
It is therefore a general object of the present invention to provide an improved method and apparatus for performing 3-dimensional antibiotic susceptibility tests.
Another object of the present invention is to provide a method for performing an antibiotic susceptibility test which provides information about both the antimicrobial activity of an antibiotic and the ability of microorganisms to inactivate antibiotics.
A further object of the present invention is to provide an apparatus for performing a 3-dimensional susceptibility test which will distribute a uniform amount of inoculum into an agar plate.
Still a further object of the present invention is to provide an apparatus for performing a 3-dimensional susceptibility test which will deposit inoculum into a slit in agar on a test plate.
Yet a further object is to provide an apparatus for performing a 3-dimensional antibiotic susceptibility test which is simple to operate.
These and other objects will be apparent to those skilled in the art.